The present invention relates to a collision time estimation apparatus for vehicles that is provided in a vehicle and estimates the time of collision with an object, and also to a collision time estimation method for vehicles. The present invention further relates to a collision alarm apparatus and a collision alarm method for vehicles that estimate the time of collision with an object having the possibility of collision with a subject vehicle, and based on the estimation result, raise an alarm of the possible collision for a driver or control the vehicle in order to avoid the collision with the object.
As disclosed in Japanese Patent Application Laid-Open No. H11-353565, conventionally, there is a collision time estimation apparatus for vehicles that detects horizontal or vertical edges of an object having the possibility of collision, from two images of surrounding areas of a vehicle which are picked up at different times, then calculates an optical flow of the detected edges using a correlation method, and estimates the time of collision with an object based on the calculated optical flow. According to such a collision time estimation apparatus for vehicles, an alarm raised based on the estimated collision time can make a driver take an action for avoiding the collision with the object.
Further, as disclosed in Japanese Patent Application Laid-Open No. H11-353565, conventionally, there is also a collision alarm apparatus for vehicles that detects horizontal or vertical edges of an object, from two images of surrounding areas of a vehicle which are picked up at different times, then calculates an optical flow of the detected edges, subsequently determines the possibility of collision with the object around the vehicle by further calculating the time of collision with the object based on the calculated optical flow, and finally raises an alarm. According to such a collision alarm apparatus for vehicles, an action for avoiding the collision with the object can be taken by a driver.
The above correlation method is a block matching algorithm of dividing an image into a plurality of areas and finding similar areas from temporally successive images. In this algorithm, when a noticeable area within the frame at time t is represented as I (x, y, t) and an area within the frame temporally successive to the frame at time t and corresponding to the noticeable area I (x, y, t) is represented as I (x+u, y+v, t+1), (u, v) to minimize the value of ΣΣ{I(x, y, t)−I(x+u, y+v, t+1)}2 and the value of ΣΣ|I(x, y, t)−I (x+u, y+v, t+1)| is detected as an optical flow of an object between the successive frames.